In wire telephony, by its very nature, the location of a caller can usually be determined from knowledge of the number assigned to the subscriber line. The principal feature of cellular radio telephony is that the caller can be anywhere within an assigned service area, which in some instances means almost anywhere in the world where compatible cellular service is available.
In cellular telephony, a caller's location can be identified only as to the cell in which the caller is currently communicating, though no provisions for reporting and tracking location are ordinarily provided in such systems. Cells are defined by coverage of individual base station antennas, and at a given base station site are commonly divided, like wedges of a pie, through use of co-located directional base-station transmitting and receiving antennas, each antenna serving an angular sector of, for example 120 degrees around the antenna site.